Humans are the only animals who display loyalty to individuals we don't personally know. Scientists had assumed this was a new development made possible by the rise of centralized governments. But it might actually be part of how we evolved.

No country could exist - indeed, no group larger than a small village could exist - without the human ability to form allegiances with total strangers. All other animal species are fundamentally distrustful of any individuals outside their immediate social groups. Until now, this was considered a byproduct of the development of complex human societies, as humans were forced to learn how to trust strangers as technological innovations brought more and more humans into regular peaceful contact.

But a nomadic group in east Africa tells a different story. The Turkana people were recently interviewed by UCLA researchers Sarah Mathew and Robert Boyd. They spoke with 118 men in the ethnic group about their customs. The Turkana are nomadic, living in small households that regularly move around in search of better pastures for their animals. And yet, if a group of Turkana men want to go to war and take the livestock of other, non-Turkana ethnic groups, they can quickly build up a force of several hundred men.

That's a remarkable feat, since there's no centralized Turkana government that can facilitate these communications or even provide a rallying point for all the men involved. Most of the combatants will be complete strangers to each other, and most are going to war on behalf of a few people they've never met. And these livestock raids are not without their perils - there's a 1.1% chance of being killed in any attack, 43% of all raids saw desertions before combat began, and 45% of raids saw someone act in what was later judged to be a cowardly fashion.

Those last bits might actually explain how the Turkana are able to maintain these combat allegiances. Those who deserted or were cowards in combat are punished by their community, often being tied to trees and beaten. The researchers suspect it's this fear of punishment that allows this cooperation to continue, despite all the risks.

Now, it's dicey comparing modern nomads with the hunter-gatherers of hundreds of thousands of years ago, and this definitely isn't proof that our ancient, isolated ancestors could rely on similar cooperation. However, this is evidence that such cooperation doesn't require the presence of a centralized government, and this behavior might well predate the rise of such social structures. If that's the case, the ability to cooperate strangers might be another piece of what makes our evolutionary history so unique.